For the transdermal or topical administration of active ingredients, the stratum corneum is a lipophilic barrier which limits the uptake of active ingredient. One of the most effective, and a physical method employed virtually for every systemically acting transdermal system, for lowering the barrier function of the stratum corneum is occlusion. The occlusion is achieved through the use of virtually water vapor-impermeable materials for the backing layers of transdermal systems, and/or through the use of water vapor-impermeable formulations of adjacent layers and/or the active ingredient layer or layers. A schematic representation of a patch of this kind is shown by FIG. 1. For the backing layers, polyester films are used in the great majority of cases. In principle, however, there is nothing against other films of low water vapor permeability, such as films of polyethylene or polypropylene, for example. As polymers or pressure-sensitive adhesives with low water vapor permeability, for example, polyisobutylene or block polymers of styrene and butadiene or of styrene and isoprene are used.
Topical systems with, for example, nonsteroidal anti-inflammatory drugs, especially, have a size which corresponds to the area of the treatment zone, and hence a size which necessitates a certain stretchability on the part of the patch system in order to increase wear comfort. Since, in the thickness appropriate for this purpose, the aforementioned occlusive materials for the backing layer do not possess sufficient stretchability or elasticity, textile materials are often employed for such patches. A disadvantage of these textile backing layers, however, is that their open porosity gives them very high water vapor permeability, meaning that they do not create occlusive conditions. As a consequence of this, occlusion in the case of patches with textile backing layers must be achieved through other water vapor-impermeable layers, or at least other layers which are less permeable to water vapor. For this purpose, of course, it is not possible to use nonstretchable and inelastic materials. The simplest way of achieving occlusion is through the use of pressure-sensitive adhesives of low water vapor permeability, such as pressure-sensitive adhesives based on polyisobutylene or on block polymers of styrene and butadiene or isoprene. A disadvantage in that case, however, is that these pressure-sensitive adhesives attach only very poorly to the skin, which becomes moist under occlusion, and are easily wholly or partly detached, especially in the joint region.
WO 01/91718 A2 describes a two-phase matrix, where a polyacrylate phase containing active ingredient is dispersed in an outer, self-adhesive formulation based on polyisobutylene or styrene-butadiene-styrene block polymers. A disadvantage here is that the occlusion effect is always at its maximum at practical layer thicknesses, and the outer phase, as already stated above, adheres very poorly to moist skin. The only advantage of such a matrix is that the active ingredient is located in a polymer with a relatively high saturation solubility.
Polyacrylate adhesives or silicone adhesives perform substantially better under such conditions, but their high water vapor permeability means that they are unable themselves to create occlusive conditions. In accordance with the prior art, therefore, the use of polyacrylate or silicone adhesives has been considered to necessitate multilayer matrices with layers differing in their composition, thereby complicating the production process and pushing up the production cost, which is an important factor for this product group.